This invention relates generally to a technique of joining an electrically-conductive elongate member to an electrically-conductive termination component and, more particularly, to a technique for laser welding the member to the component. In one application, which is not intended to be restrictive of the invention, the novel technique is provided for conductively interconnecting electrical components in an implantable medical device such as a pacemaker, a defibrillator, or the like.
Implantable stimulation devices of the type having electrical circuit components are well known in the medical arts. In one particularly common form, the implantable stimulation device comprises a pacemaker unit having an appropriate electrical power supply and related control circuitry for use in electrically stimulating a patient muscle, such as the heart. Such pacemaker units commonly include a hermetically sealed case or housing within which the power supply and control circuitry are protectively encased, in combination with one or more conductive pacemaker leads extending from the housing to the selected muscle structure within the patient. Feed-through terminals on the pacemaker housing accommodate the hermetically sealed passage of electrical conductors to the housing exterior for appropriate connection to the pacemaker lead or leads, typically through the use of so-called connector blocks having set screws or the like for secure lead attachment. The connector blocks and associated feed-through conductors disposed externally of the pacemaker housing are commonly encased within a sealed head structure, such as an insulative head of cast epoxy or the like.
The commonly used form of welding which has heretofore been satisfactory for making connections in implantable stimulation devices between leads and either electrodes or connectors has been resistance welding which unfortunately is operator dependent with many variables including electrode wear, force, and voltage. The inventors and others have come to recognize that laser welding would be desirable for joining small diameter wire to electrodes and connectors, notwithstanding the fact that resistance welders are less expensive than laser welders.
In many instances, the present laser weld design concepts for joining small diameter wire, rod or coiled wire to electrodes and connectors cannot be used to reliably produce a joint. Components made from dissimilar materials having different melting temperatures, normal component fabrication variability, insignificant thermo-mass inherent with certain components, imprecise component alignment during assembly, and unlike materials with distinctly different melting temperatures, are all major factors that affect the reliability and repeatability of weld connections using conventional design concepts.
Typical of more recent developments in this regard is the disclosure presented in U.S. Pat. No. 5,458,629 to Baudino et al. In this instance, a ring electrode may be introduced onto an insulated lead so as to form an isodiametric lead construction. The outer layer of insulation forming the lead body is etched or notched, for example, by being laser etched or physically milled to provide a recess in the lead insulation having a depth corresponding to the thickness of the ring electrode intended to be provided at that location. A ring electrode is introduced onto the notched section on the lead in the form of a C-shaped sleeve adaptable to be introduced onto the notched portion of the lead and subsequently formable into a cylindrical shape when closed into position in the notched portion of the lead so that the edges of the C-shaped sleeve are brought to an abutting as opposed to overlapping relationship. A single conductor is brought through the insulation and aligned with a hole in the C-shaped sleeve to be welded to the sleeve, for example, by laser welding. The final affixation procedure involves laser welding the abutting surfaces of the sleeve together, thereby securely forming a ring electrode isodiametrically within the notch on the electrode.
Following Baudino et al., Mueller et al., in U.S. Pat. No. 5,869,804, disclosed an improved technique of welding an electrically-conductive termination component having first and second opposed surfaces to an electrically-conductive elongate member extending to a terminal end. That method comprises the steps of forming a substantially circular aperture through the termination component and defined by a rim having a diameter substantially equivalent to the transverse dimension of the elongate member. The terminal end of the elongate member is positioned proximate the termination component overlying the rim of the aperture such that the longitudinal axis of the elongate member is generally coplanar with the center of the aperture. Then, a laser beam is directed transversely of the termination component through the aperture therein toward and onto the elongate member to simultaneously melt the elongate member and the termination component in the region of the aperture and create a mixture of the molten material of both the elongate member and the termination component within the aperture. Upon the cessation of operation of the laser beam, the mixture of the molten material solidifies within the aperture and between the termination component and the elongate member to thereby achieve a welded connection between the elongate member and the termination component. In a preferred embodiment, a ball member is formed at an end of the elongate member and the rim of the aperture in the termination component has a diameter smaller than that of the ball member and the ball member is positioned in engagement with the rim of the aperture.
More specifically, in the Mueller et al. patent, either a regular wire, coiled wire or rod, is joined to a larger termination component by means of a laser welded ball and socket joint. The elongate material is fabricated with a spherical end to increase the thermo-mass and laser target assembly. The termination component (i.e., electrode or connector) is fabricated with a target construction hole somewhat smaller than the diameter of the ball. The target hole is located where the joint will be made. Assembly is accomplished by locating the ball in the target hole forming a ball and socket assembly. The assembly is completed by directing the laser through the opposite side of the target hole, directly at the top of the ball. The laser energy melts and fuses the ball and material surrounding the target hole. A capillary effect draws the molten material into the hole resulting in a concave weld fillet.
Other previously successful techniques employing lasers for the effective termination of electrical junctions for implantable medical devices are disclosed in U.S. Pat. No. 5,282,841 to Szyszkowski and U.S. Pat. No. 5,103,818 to Maston et al.
It was with knowledge of the foregoing that the present invention has been conceived and is now reduced to practice.
The present invention relates to a technique of joining an electrically-conductive elongate member, which may be a multi-strand cable, to an electrically conductive electrode, possibly for an implantable medical device. This technique requires that the free end of the electrically-conductive elongate member be inserted axially into a longitudinally extending passage of a tubular crimp/weld sleeve. Thereupon, the crimp/weld sleeve is crimped onto the electrically-conductive elongate member to achieve firm engagement between the crimp/weld sleeve and the electrically-conductive elongate member. The crimp/weld sleeve is provided with a radially outward extending prominent member which may be one of a variety of shapes. The electrode is tubular, overlies the outer surface of a longitudinally extending lead body, and is formed with an aperture defined by a rim having a transverse dimension greater than the transverse dimension of the prominent member. The crimp/weld sleeve is received in a recess adjacent the outer peripheral surface of the lead body and the prominent member is inserted into the aperture of the tubular electrode. A laser beam is directed transversely through the aperture of the electrode and onto the prominent member to simultaneously melt the prominent member and the electrode in the region of the aperture and create a mixture of the molten material of both the prominent member and the electrode within the aperture. When operation of the laser beam ceases to allow solidification of the mixture of the molten material within the aperture, a welded connection between the crimp/weld sleeve and the electrode is achieved.
In short, a unique protrusion feature is integrated onto the outside surface area of the weld/crimp sleeve. In this design, this feature could be a weld tab, a dome-shaped knob, or a cylindrical post at or near the end of the sleeve away from the crimp zone. In the assembly set-up, the ring electrode is installed over the crimp/weld sleeve and locked in place where the hole of the ring electrode snaps onto the protrusion feature of the sleeve. This provides a reliable set-up for the following step, the laser weld operation. In this manner, a simple cable conductor termination/connection is performed by a simple and reliable connection assembly process.
Accordingly, a primary feature of the present invention is the provision of a technique for reliably welding an electrically-conductive elongate member to an electrically-conductive termination component and, more particularly, for laser welding the member to the component.
Another feature of the invention is a technique for conductively interconnecting electrical components in an implantable medical device such as a pacemaker, a defibrillator, or the like.
Still another feature of the present invention is the provision of such a technique which includes steps of providing an elongated crimp/weld sleeve having a longitudinally extending passage for axially receiving the electrically-conductive elongate member, inserting a free end of the electrically-conductive elongate member into the passage of the crimp/weld sleeve, crimping the crimp/weld sleeve onto the elongate member to achieve firm engagement between the crimp/weld sleeve and the elongate member, forming a radially outward extending prominent member on the crimp/weld sleeve, forming in the termination component an aperture defined by a rim having a transverse dimension greater than the transverse dimension of the prominent member, inserting the prominent member into the aperture of the termination component, directing a laser beam transversely of the termination component through the aperture therein and onto the prominent member to simultaneously melt the prominent member and the termination component in the region of the aperture and create a mixture of the molten material of both the prominent member and the termination component within the aperture, and discontinuing operation of the laser beam to allow solidification of the mixture of the molten material within the aperture to thereby achieve a welded connection between the crimp/weld sleeve and the termination component.
Yet another feature of the present invention is the provision of such a technique wherein the electrically-conductive elongate member includes a lead comprised of a multi-strand cable, each with a free end and wherein each free end of the multi-strand cable is inserted into the passage of the crimp/weld sleeve.
Still a further feature of the present invention is the provision of such a technique wherein the aperture is formed large enough to allow the laser beam to pass therethrough yet small enough to allow the simultaneous melting of the rim of the aperture and the termination component.
Yet a further feature of the present invention is the provision of such a technique wherein the termination component is a cylinder having an inner peripheral surface proximately received on a lead body and wherein the crimp/weld sleeve is positioned within the cylinder such that the longitudinal axis of the crimp/weld sleeve is parallel to a longitudinal axis of the cylinder.
Still another feature of the present invention is the provision of such a technique wherein, in one instance, the prominent member is a radially outward extending cylindrical post, wherein in another instance, a pair of longitudinally-extending spaced-apart cuts through the crimp/weld sleeve define a tab member which, when bent about a transverse fold line, projects radially outward from the crimp/weld sleeve and wherein, in still another instance, the crimp/weld sleeve includes an outer peripheral surface and a peripheral flange lies in a plane extending transverse of the longitudinally extending passage axis and projecting radially outward beyond the outer peripheral surface thereof and wherein the termination component has a transversely extending slot for freely receiving a portion of the peripheral flange therein.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.